A magnetic separation technique developed by researchers at Duke University's Pratt School of Engineering and Purdue University makes it relatively simple to sort through beads hundreds of times smaller than the period at the end of this sentence.
The method could lead to new technologies for medical or environmental testing, according to the researchers. For example, specially coated magnetic particles designed to attract particular viruses or bacteria might be used in tailored combinations to simultaneously test for multiple infectious pathogens in a blood or water sample.
Benjamin Yellen, assistant professor of mechanical engineering and materials science at Duke, and Gil Lee, associate professor of chemical engineering at Purdue, report their findings in the December issue of the journal Lab on a Chip (see http://www.rsc.org/Publishing/Journals/LC/article.asp?doi=b713547e).
"If there were five viruses that a patient might have been exposed to, you could potentially develop a technique to look for those five viruses all at the same time," Yellen said. In principle, such a test could be done with just a single drop of blood, as long as there was virus in the sample.
As an initial demonstration of the concept, the researchers attached two "model pathogens," a baker's yeast and a soil bacterium, to magnetic beads, and used their technique to selectively isolate them.
The magnetic separation method, which the researchers call magnetophoresis, uses a rotating magnetic field and a microchip containing an array of miniature magnets to separate tiny magnetic beads based on their size within a matter of minutes.
The physics behind the technique is as interesting as its potential applications, Yellen added. "The method causes certain particles to become essentially immobile -- just jittering back and forth -- while others move off the chip where they can be isolated. It implies that we could achieve effectively infinite separation between particle types. We thought our technique would work well for bioseparation, but we hadn't predicted it would be this good."